1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device, a method of manufacturing the same, and a method of driving the same suitable for a liquid crystal display device of an active matrix type.
2. Description of the Prior Art
A liquid crystal display panel for a conventionally general active matrix liquid crystal display device is expressed by an equivalent circuit shown in FIG. 1. More specifically, gate bus lines G1 to G4 and drain bus lines D1 to D4 are arranged to perpendicularly intersect each other, and a transistor 1 and a display pixel 2 are connected to each of their intersections. Each display pixel 2 is connected to a common electrode 3.
This active matrix liquid crystal display device is driven by drive signals shown in FIG. 3 in order to display a display pixel array dij (i, j=1, 2, 3, . . . ) as shown in FIG. 2. More specifically, one of the gate bus lines G1 to G4 is set at high level to turn on the corresponding transistors, and data on the drain bus lines D1 to D4 are written in the corresponding display pixels. This operation is sequentially performed for the gate bus lines G1 to G4, so that the liquid crystal display panel performs display with its display pixels.
In this manner, in the conventionally general active matrix liquid crystal display device, one drain bus line driving driver is required for each intersection of the gate bus lines G1 to G4 and drain bus lines D1 to D4 arranged to form a matrix.
Since the drain bus line driving driver covers a wide frequency range such as that of an image signal and operates at a high data rate, it is expensive. When the number of display pixels increases, a large number of expensive drain bus line driving drivers must be used, and the resultant liquid crystal display device becomes expensive.
In order to eliminate these drawbacks, for example, Japanese Unexamined Patent Publication Nos. 3-38689, 6-148680, and 4-269791 disclose the following techniques.
The outline of the technique of Japanese Unexamined Patent Publication No. 3-38689 will be described with reference to FIGS. 4 to 6. FIG. 4 is an equivalent circuit diagram of a liquid crystal panel, FIG. 5 is a view showing the display data arrangement, and FIG. 6 is a timing chart for displaying the data arrangement of FIG. 5.
Referring to FIG. 4, two columns of display pixels are connected to one drain bus line D1 or D2, and gate bus lines G1 to G8 are connected to the transistors on one drain bus line D1 or D2.
In this case, as shown in FIG. 6, the gate potentials of the gate bus lines G1, G3, G5, and G7 are set at high level and subsequently the gate potentials of the gate bus lines G2, G4, G6, and G8 are set at high level, so that the transistors aligned on the bus line are turned on. Data on the drain bus line D1 or D2 is written in the display pixel at this ON timing.
As shown in FIG. 5, on the drain bus line D1, data are written in d11, d21, d31, and d41 on the first display pixel column, and subsequently in d12, d22, d32, and d42 on the second display pixel column. Data write is performed on the other drain bus line D2 in the same manner.
According to this method, one drain bus line D1 or D2 can drive two display pixel columns. As a result, the number of drivers for the drain bus lines D1 and D2 can be halved, so that the product cost can be reduced.
The technique shown in Japanese Unexamined Patent Publication No. 6-148680 also aims at reduction of the product cost by increasing the number of gate bus lines while decreasing the number of expensive drain bus lines.
The outline of the technique shown in Japanese Unexamined Patent Publication No. 4-269791 will be described with reference to the equivalent circuit diagram of the liquid crystal panel shown in FIG. 7.
Display signal electrodes that form a liquid crystal signal-side drive circuits have transfer gates QT, driving transfer gates Q, and capacitors CL serving as line memories in units of columns. Each of display signal terminals VD1 to VD40 is connected to either the source electrodes or drain bus lines of the plurality of transfer gates QT. Each of selection signals "PHgr"1 to "PHgr"48 is connected to the gate electrodes of the plurality of transfer gates QT.
Note that an arbitrary one of gate voltage terminals VG1 to VG180 serving as scanning-side extending electrodes is selected, and one gate bus line is selected.
While one gate bus line is selected, selection signals are supplied to the selection signal terminals "PHgr"1 to "PHgr"48 sequentially. While one selection signal terminal "PHgr"i(i=1, 2, 3, . . . ) is selected, display signals corresponding to 40 columns are supplied to the display signal terminals VD1 to VD40, to write data in capacitors Ci (i=1, 2, 3, . . . ) serving as memory cells.
Furthermore, the liquid crystal cells LC are driven through the driving transfer gates Q. When this operation is performed 48 times, display data is written in all the liquid crystal cells LC forming a 1-line display portion.
According to the technique shown in Japanese Unexamined Patent Publication No. 4-269791, cost reduction is realized by decreasing the number of drivers on the drain bus lines without increasing the number of drivers on the gate bus lines.
In Japanese Unexamined Patent Publication Nos. 3-38689 and 6-148680 described above, although the number of drain bus drivers is decreased, the number of gate drivers is increased. Hence, further improvements are needed to achieve cost reduction of the liquid crystal display device.
According to Japanese Unexamined Patent Publication No. 4-269791, the ON resistances of transfer gates Q and QT and the capacitances of capacitors CL serving as memory cells in one liquid crystal panel vary due to the manufacturing process. Then, variations occur in the image signal voltage, leading to non-uniform brightness. Times held by the capacitors CL connected to the selection signal terminals and serving as the memory cells differ, possibly causing non-uniform brightness.
The present invention has been made in consideration of the above situation of the prior art, and has as its object to provide an active matrix liquid crystal display device which can improve the brightness uniformity without causing an increase in cost when manufacturing the device, a method of manufacturing the same, and a method of driving the same.
In order to achieve the above object, according to the first main aspect of the present invention, there is provided an active matrix liquid crystal display device comprising: a pair of substrates that seal a liquid crystal; thin film transistors arranged on one of the substrates to form a matrix of n rowsxc3x97m columns; display pixel electrodes connected to source electrodes of the thin film transistors in one-to-one correspondence; m/s (s and m are natural numbers that render m/s a natural number) drain bus lines connected to drain electrodes of the matrix-type thin film transistors in s-to-1 correspondence; sxc3x97n gate bus lines connected to gate electrodes of the thin film transistors on each row in one-to-one correspondence; and a controller for selecting n gate bus lines in each of s frames starting from an (sxc3x97t(t is an arbitrary positive integer)+1)th frame and ended with an (sxc3x97t+s)th frame, to perform one-screen display with the s frames.
According to the first main aspect described above, gate selection TFTs having drain electrodes, source electrodes, and gate electrodes can be provided, the drain electrodes in units of gate bus lines being connected to gate terminals, the source electrodes being connected to the gate bus lines, and the gate electrodes being connected to gate switch lines that are set at an ON voltage in one frame every s frames.
The gate selection TFTs can be formed simultaneously with the thin film transistors connected to the display pixel electrodes in the same process.
A semiconductor film which forms the gate selection TFTs can be made of amorphous silicon, and can have a ratio of channel length to channel width of not less than 3000/4.
A gate ON voltage for the gate selection TFTs can be not less than 30 V, and a gate OFF voltage therefor can be not more than xe2x88x9210 V.
A semiconductor film which forms the gate selection TFTs can be made of polysilicon.
The gate electrodes of the gate selection TFTs can be switched within a blanking period.
One frame can be drawn with a time of 1/(50xc3x97n) to 1/(75xc3x97n) sec.
In order to achieve the above object, according to the second main aspect of the present invention, there is provided a method of manufacturing an active matrix liquid crystal display device, comprising: the first step of forming thin film transistors arranged to form a matrix of n rowsxc3x97m columns on one of a pair of substrates that seal a liquid crystal; the second step of forming display pixel electrodes connected to source electrodes of the thin film transistors in one-to-one correspondence; the third step of forming m/s (s and m are natural numbers that render m/s a natural number) drain bus lines connected to drain electrodes of the matrix-type thin film transistors in s-to-1 correspondence; and the fourth step of forming sxc3x97n gate bus lines connected to gate electrodes of the thin film transistors on each row in one-to-one correspondence.
In the second main aspect described above, the fourth step can comprise the fifth step of connecting gate terminals to the drain electrodes in units of gate bus lines, the sixth step of connecting the gate bus lines to the source electrodes; and the seventh step of connecting gate switch lines to the gate electrodes, the gate switch lines being set at an ON voltage in one frame every s frames.
The fifth to seventh steps can be performed simultaneously with formation of the thin film transistors connected to the display pixel electrodes in the same process.
The fifth to seventh steps can include the step of forming a semiconductor film from amorphous silicon to have a ratio of channel length to channel width of not less than 3000/4.
The fifth to seventh steps can include the step of forming a semiconductor film from polysilicon.
In order to achieve the above object, according to the third main aspect of the present invention, there is provided a method of driving an active matrix liquid crystal display device, comprising driving the display device by setting a gate ON voltage for gate selection TFTs to not less than 30 V, and setting a gate OFF voltage therefor to not more than xe2x88x9210 V.
In the third main aspect described above, driving can be performed such that the gate electrodes of the gate selection TFTs are switched within a blanking period.
Driving can be performed such that one frame is drawn with a time of 1/(50xc3x97n) to 1/(75xc3x97n) sec.
As described above, with the active matrix liquid crystal display device, a method of manufacturing the same, and a method of driving the same according to the present invention, the thin film transistors are arranged on one of the pair of substrates that seal the liquid crystal to form a matrix of n rowsxc3x97m columns. Display pixel electrodes are connected to source electrodes of the thin film transistors in one-to-one correspondence. M/s (s and m are natural numbers that render m/s a natural number) drain bus lines are connected to drain electrodes of the matrix-type thin film transistors in s-to-1 correspondence. Sxc3x97n gate bus lines are connected to gate electrodes of the thin film transistors on each row in one-to-one correspondence. A controller selects n gate bus lines in each of s frames starting from an (sxc3x97t(t is an arbitrary positive integer)+1)th frame and ended with an (sxc3x97t+s)th frame. One-screen display is performed with the s frames. Therefore, the brightness uniformity can be improved without increasing the cost of the device.